1. Field of the Invention
The present invention relates to a nickel-zinc alkaline storage battery in which nickel oxide is used as the active material of the positive electrode, and zinc as the active material of the negative electrode and more particularly, it provides a battery of long life and low price which produces only small amount of dendritic crystals of zinc, by controlling the amount of alkaline electrolyte and improving the separating member.
2. Description of the Prior Art
Zinc has low atomic weight relative to those of other metals used as the active materials of the negative electrode of storage batteries, is electrochemically base, shows high hydrogen overvoltage, is low polluting and is still low priced; accordingly, it is suitable as an electrode material giving high energy density, high output, low self-discharge, low polution and low price. It is defective, however, in that because the discharge product dissolves in the electrolyte, the repetitive charge-discharge often causes disfiguration of the electrode, and short-circuiting due to the development of the dentritic crystals during charging, and consequently, such electrode made of zinc is shortlived.
Many studies have been carried out in order to eliminate these disadvantages while preserving the advantages. First of all for the prevention of the development of the dendritic crystals, the employment of additives in the electrode and/or electrolyte, stirring or circulating the electrolyte, charging by use of inverse current pulse or meta-stable voltage, use of electrolytes other than KOH such as amine baths, etc., have been proposed, and for the prevention of the disfiguration of the electrode, stirring or circulating the electrolyte, placing the electrode horizontally, making the discharge product insoluble, etc., have been offered.
It is believed, as described later, that the growth of the dendritic crystals results from the fact that the zincate ion in the solution deposits on the projected part if its supply to the electrode surface is not adequate, and since the additive does not serve to remove the direct cause, the complete prevention of the development of the dendritic crystals cannot be expected from its use. The method of stirring or circulating the electrolyte or the method of placing the electrode horizontally is disadvantageous in that the use of equipment which is complex, or is not portable in usual manner, is required. In the charging method, the use of chargers which are complex and high priced is unavoidable. The method of using as the electrolyte, an amine bath or the method of making the discharge product insoluble degrades the discharge characteristics.
As described hereabove, it was very difficult to lengthen the charge-discharge cycle life of the zinc negative electrode in alkaline solution.
According to this invention, the improvement in the charge-discharge cycle life is achieved by controlling the amount of the electrolyte, so that the free electrolyte may be eliminated, and by improving the separating member. In the case of nickel-zinc alkaline storage batteries, the batteries were short-lived due to the degradation of the zinc negative electrode, while the characteristics of the nickel positive electrode were excellent. Accordingly, the life of the nickel-zinc alkaline storage batteries would necessarily be lengthened by improving the life of the zinc negative electrode.